It sounds as though you have not installed Maptech coverage specifically for the area in question. Each Maptech nautical chart CD provides multiple scales of coverage in a given ChartKit Region. Often, the small-scale charts will cover not only the specific area you purchased, but will also extend beyond to areas for which you have not purchased detailed charts. You may be looking at such a location.

Press the Scale button at the lower right of the screen for a list of all chart scales available at your location. If the list is empty, no other scales are available.